In recent years, air conveyors have become popular for conveying lightweight articles, such as cylindrical lightweight beverage containers, both during the manufacturing of the containers and during the filling operation. Such conveyors have enjoyed considerable success because they allow the conveying of the containers at a much higher speed than was possible with mechanical conveyors. These air conveyors have used, in various forms, air jets and louvers for moving the containers along the conveying surface. The angle at which air is introduced to the conveying surface has included jets or louvers directing the air parallel to the direction of movement as well as various angles transversely to the direction of movement. In general, it has been the intent of these devices to use the blowing force of the air to move the containers in the desired direction.
Also, devices have been developed by the invention in which air is supplied through air jets in a manner to take advantage of the Coanda Effect to cause the air to move along the surface of the conveyor and therefore along the lower surface of the container on the conveyor. This effect, together with utilizing the Bernoulli Principle, is utilized to create low pressure in the areas at which the air flows at the highest velocity so as to maneuver the containers in response to changes in air pressure rather than relying on the ability of the device to blow the containers in the desired direction. These principles have been used to create desired high and low pressure areas between adjacent containers to regulate their flow.
Barker, U.S. Pat. No. 3,105,720, shows the use of louvers at opposite ends of cylindrical containers for moving them vertically from one conveyor to another.
Futer, U.S. Pat. No. 3,180,688, discloses a mass conveyor which utilizes a series of louvers and vertical jets. The vertical jets suspend the articles above the conveyor while the louvers provide a downstream propelling force for moving the articles in the downstream direction.
Malmgren et al., U.S. Pat. No. 3,385,490, disclose a device for conveying web or sheet material along a conveyor in which louvers are provided which are angled inwardly from the outboard edges of the conveyor toward the center. An exhaust grid is provided at the center of the device for evacuation of air. This device is intended to center a sheet of material and convey it downstream due to the downstream force component of the air passing through the louvers. The inboard component of the air from the louvers is intended to be equal on both sides and therefore center the sheet material over the conveyor.
Fong, U.S. Pat. Nos. 3,733,056 and 4,033,555, each disclose a conveyor for fluidizing particulate material and utilizes louvers pointed in both a downstream direction and a direction substantially transversely to the direction of movement.
Hassan et al. U.S. Pat. No. 4,165,132, disclose an air conveyor for conveying semiconductor wafers wherein air jets are provided at an inboard angle from the side edges of the conveyor for suspending and centering the wafers over the conveyor. These jets also create a downstream force component which moves the wafer along the conveyor in the downstream direction.
Lenhart, U.S. Pat. No. 4,456,406, discloses a mass conveyor requiring a top cover and utilizes the formation of high pressure areas between articles to form air barriers for the containers to maintain them in a loose separate condition as they move through the conveyor. This is to minimize banging of the containers against each other and potential damage to them due to this banging action.
Lenhart, U.S. Pat. No. 4,732,513, provides a coverless air conveyor in which jets are provided through the conveying surface in a substantially vertical direction with a slight downstream tilt. Side walls are provided to form air dams to create a flowing body of air which enveloped and lifted the respective containers and moved them at a desired speed. However, if any adjustment is desired in the speed of movement of the mass of containers, it is necessary through dampers to vary the volume of air passing through the jets.
All of the foregoing inventions are suitable for their intended purposes. However, in order to control the flow of the articles on the conveyor, it is necessary to provide dampers at various positions along the plenum in order to control the amount of air issuing through the air jets or louvers of any particular location along the conveying surface. This is necessary in order to change the speed of the movement of the articles from one portion of the conveyor to the next to minimize potential damage to the containers as they move from one operative station to another. When using dampers in an effort to control the speed of an article, as the static pressure is varied upward and downward, the velocity from the deck louvers varies accordingly, and as the velocity varies the volume also varies. This makes control very difficult because of the two parallel variables. If the pressure is set too low in an attempt to slow the speed of the article, the article will not be levitated sufficiently above the deck surface and cannot be conveyed. Conversely, if the pressure is set too high, in order to convey the article at the higher speed, the article will be levitated too high above the deck and may wobble, so that it does not flow smoothly down the air conveyor and may tip over, creating a jam along the conveyor.
Furthermore, with the mass air conveyors discussed above, as an article moves from an upstream location to a downstream location, the volume of air acting on each container increases thereby tending to move the articles at greater and greater speeds, toward a terminal velocity. This is particularly true with single or sparse containers moving along the conveyor. Such a condition can result in articles striking each other with sufficient force to cause damage to fragile articles, such as beverage containers.